System and method for controlling an exhaust system having a selective catalyst reduction component

ABSTRACT

A method for controlling operation of an SCR component includes receiving a signal reflecting a sensed condition of an exhaust stream associated with the SCR component, estimating an apparent aging time of the SCR component based on the sensed condition of the exhaust stream, and setting an operating condition of the SCR component based on the apparent aging time of the SCR component.

FIELD OF THE INVENTION

The subject invention relates to vehicle exhaust systems, and more particularly to systems and methods for controlling exhaust systems that include a selective catalyst reduction (SCR) components.

BACKGROUND

The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

During combustion in a diesel engine, an air/fuel mixture is delivered through an intake valve to cylinders and is compressed and combusted therein. After combustion, the piston forces the exhaust gas in the cylinders into an exhaust system. The exhaust gas may contain oxides of nitrogen (NOx) and carbon monoxide (CO).

Exhaust gas treatment systems may employ catalysts in one or more components configured for accomplishing an SCR process such as reducing nitrogen oxides (NOx) to produce more tolerable exhaust constituents of nitrogen (N2) and water (H2O). Reductant may be added to the exhaust gas upstream from an SCR component, and, for example only, the reductant may include anhydrous ammonia (NH3), aqueous ammonia or urea, any or all of which may be injected as a fine mist into the exhaust gas. When the ammonia, mixed with exhaust gases, reaches the SCR component, the NOx emissions break down. A Diesel Particulate Filter (DPF) may then capture soot, and that soot may be periodically incinerated during regeneration cycles. Water vapor, nitrogen and reduced emissions exit the exhaust system.

To maintain efficient NOx reduction in the SCR component, a control may be employed so as to maintain a desired quantity of the reductant (i.e., reductant load) in the SCR component. As exhaust gas containing NOx passes through the SCR component, the reductant is consumed, and the load is depleted. A model may be employed by the control to track and/or predict how much reductant is loaded in the SCR component and to maintain an appropriate reductant load for achieving a desired effect such as reduction of NOx in the exhaust stream. The model may also be employed to determine aging of the SCR component so as to facilitate periodic servicing or to adapt control over the engine and SCR systems so as to achieve selected objectives. Proper assessment of aging of the SCR component can facilitate advantageous control over the SCR component so as to achieve desirable SCR efficiencies and beneficial trade-offs between engine operability, power output, fuel consumption, and NOx emission, resulting in improved performance and/or fuel economy and reduced urea consumption.

Unfortunately, determining aging of an SCR component onboard a vehicle can be costly and unreliable. For example, conventional methods may rely upon correlations between SCR aging rates and engine-related parameters sensed upstream from the SCR component. Yet, SCR aging may actually be more closely related to substrate temperatures in the SCR component and to other conditions internal to the SCR component, conditions that can be difficult to determine with suitable accuracy. Therefore, aging methods that are based on correlations with engine parameters that can be sensed can be costly, can require significant time to develop correlation data to fully characterize aging as a function of the numerous parameters affecting aging, and can be inaccurate if all significant variables are not considered.

Accordingly, it is desirable to provide a system and method for predicting SCR aging time onboard the vehicle without relying on sensed engine parameters and costly correlations. It is also desirable to have an improved system and method for controlling exhaust systems that include an SCR component, wherein SCR component aging may be determined based on one or more parameters directly affected by operation of the SCR component.

SUMMARY OF THE INVENTION

In one exemplary embodiment of the invention, a method for controlling operation of an SCR component includes receiving a signal reflecting a sensed condition of an exhaust stream associated with the SCR component, estimating an apparent aging time of the SCR component based on the sensed condition of the exhaust stream, and setting an operating condition of the SCR component based on the apparent aging time of the SCR component.

In another exemplary embodiment of the invention, a system for controlling operation of an SCR component comprises a selective catalyst reduction (SCR) component diagnostic module that is configured for receiving a signal reflecting a sensed condition of an exhaust stream associated with the SCR component and for estimating an apparent aging time of the SCR component based on the sensed condition of the exhaust stream. A system for controlling operation of an SCR component also comprises an SCR component management module that is configured for selectively adjusting an operating condition of the SCR component based on the apparent aging time of the SCR component.

The above features and advantages and other features and advantages of the invention are readily apparent from the following detailed description of the invention when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, advantages and details appear, by way of example only, in the following detailed description of embodiments, the detailed description referring to the drawings in which:

FIG. 1 is a functional block diagram of an engine control system including an exhaust diagnostic system that automatically predicts SCR aging time according to the present disclosure;

FIG. 2 is a functional block diagram of an exemplary implementation of a control module of the exhaust diagnostic system of FIG. 1; and

FIG. 3 illustrates a method for resetting an exhaust diagnostic system after operating with poor diesel reductant quality according to the present disclosure.

DESCRIPTION OF THE EMBODIMENTS

The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure.

As used herein, the term “module” refers to an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality.

While the following disclosure involves diesel engines, other types of engines such as gasoline engines, including direct injection engines, may benefit from the teachings herein.

In accordance with an exemplary embodiment of the invention, the present disclosure provides a system and method for predicting SCR aging time onboard the vehicle without relying on sensed engine parameters and/or correlations between SCR aging and engine-related parameters. The present disclosure also provides improved systems and methods for controlling exhaust systems that include a selective catalyst reduction (SCR) component. These improved systems and methods are enabled by the capability to determine SCR component aging, in real time, based on one or more on-board parameters that are directly affected by operation of the SCR component (e.g., NOx content of the exhaust stream downstream from the SCR component).

With SCR aging time established, control over operation of the engine system, including the SCR component, can be executed with improved accuracy and reliability. For example, dosing can be controlled to provide a suitable load of reductant on the SCR catalyst. Similarly, the exhaust diagnostic system according to the present disclosure may elevate the exhaust temperature using intrusive exhaust gas temperature management so that a temperature of the SCR catalyst is at a suitable level to facilitate desirable operation of the SCR component or, in some situations, to allow testing of the efficiency of the SCR catalyst. In some situations, it may be desirable to exercise control over the vehicle speed and/or other operating parameters.

Referring now to FIG. 1, a diesel engine system 10 is schematically illustrated. The diesel engine system 10 includes a diesel engine 12 and an exhaust treatment system 13. The exhaust treatment system 13 further includes an exhaust system 14 and a dosing system 16. The diesel engine 12 includes a cylinder 18, an intake manifold 20, a mass air flow (MAF) sensor 22 and an engine speed sensor 24. Air flows into the diesel engine 12 through the intake manifold 20 and is monitored by the MAF sensor 22. The air is directed into the cylinder 18 and is combusted with fuel to drive pistons (not shown). Although a single cylinder 18 is illustrated, it can be appreciated that the diesel engine 12 may include additional cylinders 18. For example, diesel engines having 2, 3, 4, 5, 6, 8, 10, 12 and 16 cylinders are anticipated.

Exhaust gas 19 is produced inside the cylinder 18 as a result of the combustion process. The exhaust system 14 treats the exhaust gas before the exhaust gas is released to atmosphere. The exhaust system 14 includes an exhaust manifold 26 and a diesel oxidation catalyst (DOC) 28. The exhaust manifold 26 directs exhaust exiting the cylinder through the DOC 28. The exhaust is treated within the DOC 28 to reduce the emissions. The exhaust system 14 further includes an SCR component 30, a DOC inlet temperature sensor 31, an SRC inlet temperature sensor 32, an SRC outlet temperature sensor 34 and a particulate filter (PF) 36.

The DOC inlet temperature sensor 31 may be positioned between the engine and the DOC 28. The SRC inlet temperature sensor 32 is located upstream from the SCR component 30 to monitor temperatures at the inlet of the SCR component 30. The SRC outlet temperature sensor 34 is located downstream from the SCR component 30 to monitor temperatures at the outlet of the SCR component 30. Although the exhaust treatment system 13 is illustrated as including the SRC inlet and SRC outlet temperature sensors 32, 34 arranged outside the SCR component 30, the SRC inlet and SRC outlet temperature sensors 32, 34 can be located inside the SCR component 30 to monitor temperatures of the exhaust 19 at the inlet and outlet of the SCR component 30. The PF 36 further reduces emissions by trapping particulates (i.e., soot) in the exhaust gas 19.

The dosing system 16 includes a dosing injector 40 that injects reductant from a reductant supply 38 into the exhaust gas 19. The reductant mixes with the exhaust gas and further reduces the emissions when the mixture is exposed to the SCR component 30. A mixer 41 may be used to mix the reductant with the exhaust gas upstream from the SCR component 30. A control module 42 regulates and controls the operation of the engine system 10.

An exhaust gas flow rate sensor 44 may generate a signal corresponding to the flow of exhaust 19 in the exhaust system. Although the sensor is illustrated between the SCR component 30 and the PF 36, various other locations within the exhaust system may be used for measurement including downstream from the exhaust manifold and upstream from the SCR component 30.

A temperature sensor 46 generates a particulate filter temperature corresponding to a measured particulate filter temperature. The temperature sensor 46 may be disposed on or within the PF 36. The temperature sensor 46 may also be located upstream or downstream from the PF 36.

Other sensors in the exhaust system may include an upstream NOx sensor 50 that generates a NOx signal based on a concentration of NOx present in the exhaust system. A downstream NOx sensor 52 may be positioned downstream from the PF 36 to measure a concentration of NOx leaving the PF 36 or may be positioned downstream from the SCR component 30, such as in a close-coupled arrangement. In addition, an ammonia (NH3) sensor 54 generates a signal corresponding to the amount of ammonia within the exhaust gas. The NH3 sensor 54 is optional, but can be used to simplify the control system due to the ability to discern between NOx and NH3. The downstream NH3 sensor 54 may be positioned downstream from the PF 36 to measure a concentration of NH3 leaving the PF 36 or may be positioned downstream from the SCR component 30, such as in a close-coupled arrangement. Alternately and/or in addition, a hydrocarbon (HC) supply 56 and a HC injector 58 may be provided to supply HC in the exhaust gas 19 reaching the DOC catalyst.

Referring now to FIG. 2, the control module 42 may include an SCR component diagnostic module 60 that is used to determine a conversion efficiency of NOx at the SCR component 30. The control module 42 further includes an SCR component management module 62 that intrusively controls a temperature or other parameters of the SCR component 30. In an exemplary embodiment, the SCR component diagnostic module 60 includes a signal receiver 70 and an SCR reaction simulation module 72. The signal receiver 70 is configured for receiving a signal reflecting a sensed condition of an exhaust stream associated with the SCR component. The SCR reaction simulation module 72 is configured for estimating an apparent aging time of the SCR component based on the sensed condition of the exhaust stream. In an exemplary embodiment, the signal receiver 70 of the SCR component diagnostic module 60 receives one or more signals reflecting conditions of the exhaust stream, such as a sensed NOx content of the exhaust stream and/or a sensed NH3 content of the exhaust stream downstream from the SCR component.

In an exemplary embodiment, the SCR reaction simulation module 72 of the SCR component diagnostic module 60 is configured to determine SCR component aging (e.g., through a recursive algorithm or an iterative process). For example, the SCR reaction simulation module 72 may set a model input SCR aging time and subsequently execute an SCR reaction simulation model by first determining a predicted SCR reaction efficiency based on the model input SCR aging time and then determining a predicted condition of the exhaust stream 19 based on the predicted SCR reaction efficiency. In accordance with such embodiments, the SCR reaction simulation module 72 is driven to iterate as a solution module 74 adjusts the model input SCR aging time and subsequently causes the SCR reaction simulation module 72 to predict SCR reaction efficiency based on the incremented input SCR aging time and the corresponding predicted condition of the exhaust stream. The solution module 74 continues this process until the predicted condition of the exhaust stream 19 is within a predetermined tolerance of the sensed condition of the exhaust stream 19. When the predicted condition of the exhaust stream is within the predetermined tolerance of the sensed condition of the exhaust stream (i.e., the model is converged, a solution is achieved), the solution module 74 sets an apparent SCR aging time to be equal to the model input SCR aging time.

In an exemplary embodiment, the SCR component management module 62 includes an SCR component manager 78 that is configured for selectively adjusting an operating condition of the SCR component based on the apparent aging time of the SCR component. For example, operating conditions of the SCR component may include SCR temperature, dosing rate, reductant load, EGR, and/or other pertinent operating conditions. To accomplish this, the SCR component management module 62 includes an SCR efficiency module 76 that is configured for determining an efficiency of an SCR reaction. The SCR efficiency module 76 may accomplish this, for example, by interpolating one or more empirical data tables representing an efficiency of an SCR reaction as a function of SCR aging time. Alternatively, the SCR efficiency module 76 may determine efficiency by evaluating one or more polynomial expressions characterizing reaction efficiency as a function of SCR aging time.

The SCR efficiency module 76 of the SCR component management module 62 also calculates a temperature of the SCR component. The SCR efficiency module 76 may calculate the temperature of the SCR component based on the SRC inlet temperature sensor 32, the SRC outlet temperature sensor 34, a model or any other suitable method. For example only, the SCR efficiency module 76 may calculate the SCR component temperature based on values from both the SRC inlet and SRC outlet temperature sensors 32, 34. For example only, the SCR efficiency module 76 may calculate the temperature based on an average or a weighted average of the SRC inlet and SRC outlet temperature sensors 32, 34.

The control module 42 includes a vehicle speed control module 80 that controls vehicle speed based on the SCR component efficiency (e.g., limits vehicle speed when efficiency falls below a predetermined threshold). The control module 42 further includes a fueling control module 82 that determines fuel quantity, fuel injection timing, post injection, etc. When in the intrusive SCR component test mode, the SCR component management module 62 adjusts fueling. The fueling adjustment increases a temperature of the SCR component. Alternately, a hydrocarbon injection module 84 injects fuel into the exhaust upstream from the DOC catalyst 28 to generate an exotherm to increase the temperature in the SCR component.

Referring now to FIG. 3, a method for controlling operation of an SCR component begins by determining whether it is necessary or desirable to determine an aging of the SCR component (step 100). If so, a method for controlling operation of an SCR component includes receiving a signal reflecting a sensed condition of an exhaust stream 19 associated with the SCR component (step 110). The signal may reflect a sensed NOx content of the exhaust stream (step 112) and/or a sensed NH3 content of the exhaust stream (step 114), and the signal may originate downstream from the SCR component (step 116).

A method for controlling operation of an SCR component also includes estimating an apparent aging time of the SCR component based on the sensed condition of the exhaust stream (step 120). A method for estimating an apparent aging time of the SCR component may include first setting a model input SCR aging time (step 130), and then executing an SCR reaction model (step 140). Executing an SCR reaction model may include determining a predicted SCR reaction efficiency based on the model input SCR aging time (step 142) and then determining a predicted condition of the exhaust stream based on the predicted SCR reaction efficiency (step 144). The predicted condition of the exhaust stream is compared to the sensed condition of the exhaust stream to determine whether they are sufficiently close, or within an acceptable tolerance (step 146). If not, the model input SCR aging time is adjusted (step 148) and the SCR reaction model is again executed (step 140) until the predicted condition of the exhaust stream is within a predetermined tolerance of the sensed condition of the exhaust stream. When the predicted condition of the exhaust stream is within the predetermined tolerance of the sensed condition of the exhaust stream (or when another appropriate convergence criteria) is achieved, an apparent SCR aging time is set equal to the model input SCR aging time (step 150).

In an exemplary embodiment, a predicted SCR reaction efficiency may be determined (step 160) by interpolating one or more empirical data tables representing an efficiency of an SCR reaction as a function of SCR aging time (step 162) or by evaluating one or more polynomial expressions characterizing reaction efficiency as a function of SCR aging time (step 164). Finally, a method for controlling operation of an SCR component also includes setting an operating condition of the SCR component based on the apparent aging time of the SCR component (step 170). Having improved knowledge of SCR component aging, operation of the engine and the SCR can be more advantageously controlled such as by improving SCR efficiency and optionally balancing engine fuel consumption, NOx emission, and urea consumption (step 172). The control may, for example, increase or decrease the exhaust temperature by altering fueling (fuel quantity, fuel injection timing, post injection, etc.) and/or by starting, stopping, increasing, or decreasing HC injection.

In some situations, such as when an SCR component has been determined to be of sufficient aging, control may undertake remedial measures such as disabling exhaust gas recirculation (EGR) (step 180). The control may also activate a process for depleting a reductant load to establish a reliable reductant load on the SCR component (step 182). After the reductant load has been depleted, dosing can be re-commenced to re-establish a known (i.e., reliably predictable by the reductant load model) load on the SCR component (step 184). With a known reductant load, the control may measure an efficiency of the SCR conversion process (step 186), for example, by comparing an efficiency based on upstream and downstream accumulated masses as well as upstream NOx and SCR component temperature. The control may assess quality of the reductant by comparing the measured efficiency to the efficiency determined based on aging as described above (step 188). If reductant quality is insufficient, additional remedial measures may be undertaken (step 190). These may include illumination of a warning light, imposition of vehicle speed limiting, intrusive exhaust gas temperature management, and adjustments to EGR.

Thus, an exemplary method for controlling operation of an SCR component enables use of an onboard recursive optimization algorithm to determine SCR aging time in real-time by matching output from an SCR model with signals dispatched from a NOx sensor positioned at the outlet of the SCR component or downstream from the SCR component. The SCR model determines a predicted concentration of NOx and NH3 at the outlet of the SCR component based on SCR reaction efficiency values which are determined by interpolating SCR efficiency tables with SCR aging time. An SCR aging input is floated until the predicted concentrations of NOx and/or NH3 match, with sufficient accuracy, signals dispatched from the sensors. A model may employ interpolation between data points of predetermined (e.g., based on empirical data or developed theoretically) SCR NH3 reaction efficiency tables and NH3 desorption and absorption tables covering a range of aging stages.

Accordingly, SCR aging time can be determined on-board, and adaptively, eliminating the need for the system to have knowledge of the relationship between SCR aging rate and engine parameters. By obviating the need to correlate SCR aging rate with engine parameters, substantial time and cost associated with calibration can be eliminated. In addition, the systems and methods described herein enable determination of SCR aging after a vehicle SCR is changed (e.g., due to damage). Finally, having improved knowledge of SCR component aging, operation of the engine and the SCR can be more advantageously controlled such as by improving SCR efficiency and optionally balancing engine fuel consumption, NOx emission, and urea consumption.

While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, but that the invention will include all embodiments falling within the scope of the application. 

What is claimed is:
 1. A method for controlling operation of an SCR component comprising: receiving a signal reflecting a sensed condition of an exhaust stream associated with the SCR component; estimating an apparent aging time of the SCR component based on the sensed condition of the exhaust stream; and setting an operating condition of the SCR component based on the apparent aging time of the SCR component.
 2. A method as described in claim 1, wherein said receiving a signal reflecting a sensed condition of an exhaust stream associated with the SCR component comprises receiving a signal reflecting a sensed NOx content of the exhaust stream.
 3. A method as described in claim 1, wherein said receiving a signal reflecting a sensed condition of an exhaust stream associated with the SCR component comprises receiving a signal reflecting a sensed NH3 content of the exhaust stream.
 4. A method as described in claim 1, wherein said receiving a signal reflecting a condition of an exhaust stream associated with the SCR component comprises receiving a signal reflecting a sensed condition of the exhaust stream downstream from the SCR component.
 5. A method as described in claim 1, wherein said estimating an apparent aging time of the SCR component comprises: setting a model input SCR aging time; executing an SCR reaction model comprising: determining a predicted SCR reaction efficiency based on the model input SCR aging time; and determining a predicted condition of the exhaust stream based on the predicted SCR reaction efficiency; adjusting the model input SCR aging time and subsequently executing the SCR reaction model until the predicted condition of the exhaust stream is within a predetermined tolerance of the sensed condition of the exhaust stream; and setting an apparent SCR aging time equal to the model input SCR aging time when the predicted condition of the exhaust stream is within the predetermined tolerance of the sensed condition of the exhaust stream.
 6. A method as described in claim 5, wherein said sensed condition of the exhaust stream comprises a sensed NOx content of the exhaust stream.
 7. A method as described in claim 5, wherein said sensed condition of the exhaust stream comprises a sensed NH3 content of the exhaust stream.
 8. A method as described in claim 5, wherein said sensed condition of the exhaust stream comprises a sensed condition downstream from the SCR component.
 9. A method as described in claim 5, wherein said determining a predicted SCR reaction efficiency comprises interpolating one or more empirical data tables representing an efficiency of an SCR reaction as a function of SCR aging time.
 10. A method as described in claim 5, wherein said determining a predicted SCR reaction efficiency comprises evaluating one or more polynomial expressions characterizing reaction efficiency as a function of SCR aging time.
 11. A system for controlling operation of an SCR component comprising: a selective catalyst reduction (SCR) component diagnostic module that is configured for receiving a signal reflecting a sensed condition of an exhaust stream associated with the SCR component and for estimating an apparent aging time of the SCR component based on the sensed condition of the exhaust stream; and an SCR component management module that is configured for selectively adjusting an operating condition of the SCR component based on the apparent aging time of the SCR component.
 12. A system as described in claim 11, wherein said selective catalyst reduction (SCR) component diagnostic module is configured for receiving a signal reflecting a sensed NOx content of the exhaust stream.
 13. A system as described in claim 11, wherein said selective catalyst reduction (SCR) component diagnostic module is configured for receiving a signal reflecting a sensed NH3 content of the exhaust stream.
 14. A system as described in claim 11, wherein said selective catalyst reduction (SCR) component diagnostic module is configured for receiving a signal reflecting a sensed condition of the exhaust stream downstream from the SCR component.
 15. A system as described in claim 11, wherein said selective catalyst reduction (SCR) component diagnostic module is configured for: setting a model input SCR aging time; executing an SCR reaction model comprising: determining a predicted SCR reaction efficiency based on the model input SCR aging time; and determining a predicted condition of the exhaust stream based on the predicted SCR reaction efficiency; adjusting the model input SCR aging time and subsequently executing the SCR reaction model until the predicted condition of the exhaust stream is within a predetermined tolerance of the sensed condition of the exhaust stream; and setting an apparent SCR aging time equal to the model input SCR aging time when the predicted condition of the exhaust stream is within the predetermined tolerance of the sensed condition of the exhaust stream.
 16. A system as described in claim 15, wherein said selective catalyst reduction (SCR) component diagnostic module is configured for receiving a signal reflecting a sensed NOx content of the exhaust stream.
 17. A system as described in claim 15, wherein said selective catalyst reduction (SCR) component diagnostic module is configured for receiving a signal reflecting a sensed NH3 content of the exhaust stream.
 18. A system as described in claim 15, wherein said selective catalyst reduction (SCR) component diagnostic module is configured for receiving a signal reflecting a sensed condition of the exhaust stream downstream from the SCR component.
 19. A system as described in claim 15, wherein said selective catalyst reduction (SCR) component diagnostic module is configured for interpolating one or more empirical data tables representing an efficiency of an SCR reaction as a function of SCR aging time.
 20. A system as described in claim 15, wherein said selective catalyst reduction (SCR) component diagnostic module is configured for evaluating one or more polynomial expressions characterizing reaction efficiency as a function of SCR aging time. 